We further characterized the neo-free TNF KO mice completely lacking the Peyer's patches (in collaboration with J. Berzovsky lab at NCI and W. Murphy at University of Nevada). We generated and characterized novel mice "humanized" for the TNF/LT locus. In one founder a modest overexpression of TNF/LT resulted in TNFRp55-mediated thymic athrophy. Effects of inducible ablation of either TNF or LT signalling in both pharmacological and genetic settings are being evaluated with specific focus on the integrity of lymphoid organ structure. Additonally, in collaboration with R. Zinkernagel lab in Zurich we addressed the link between the integrity of peripheral lymphoid tissues and anti-viral immunity. Finally, in collaboration with J. Keller and J. Ryan (Virginia Commonwealth University) we evaluated hematopoiesis in TNF, LT and TNF/LT knockout mice.